[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH 0/8] s390x/pci: Fixing s390 vfio-pci ISM support

From: Pierre Morel
Subject: Re: [PATCH 0/8] s390x/pci: Fixing s390 vfio-pci ISM support
Date: Thu, 21 Jan 2021 13:30:30 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0

On 1/21/21 10:58 AM, Niklas Schnelle wrote:

On 1/21/21 9:27 AM, Pierre Morel wrote:

On 1/20/21 9:29 PM, Matthew Rosato wrote:
On 1/20/21 2:18 PM, Pierre Morel wrote:


So, I mean I can change the code to be more permissive in that way (allow any 
device that doesn't have MSI-X capability to at least attempt to use the 
region).  But the reality is that ISM specifically needs the region for 
successful pass through, so I don't see a reason to create a different bit for 
that vs just checking for the PFT in QEMU and using that value to decide 
whether or not region availability is a requirement for allowing the device to 
pass through.

There is no need for a new bit to know if a device support MIO or not, as I 
said before, there is already one in the CLP query PCI function response and it 
is already used in the kernel zPCI architecture.

It is not a big think to do and does not change the general architecture of the 
patch, only the detection of which device is impacted to make it generic 
instead of device dedicated.


Just wanted to say that we've had a very similar discussion with
Cornelia end of last year and came to the conclusion that explicitly
matching the PFT is likely the safest bet:

What I see there is a discussion on the relation between relaxed access and MIO without explaining to Connie that we have in the kernel the possibility to know if a device support MIO or not independently of it supports the relaxed access.

The all point here is about taking decisions for the right reasons.

We have the possibility to take the decision based on functionalities and not on a specific PCI function.

If we keep the PFT check, and we can do this of course, but is it a good solution if it appears we have other PFT with the same functionalities?

Please note that this is a minor code change, keeping track of the MIO support just as we keep track of the PFT and check on this instead of on the PFT.

It does not modify the general architecture of the patch series neither in kernel nor in QEMU at all.


Pierre Morel
IBM Lab Boeblingen

reply via email to

[Prev in Thread] Current Thread [Next in Thread]